A file picture of a North Korean Hwasong-14 intercontinental ballistic missile test launched last month.

By Sarah Zheng

China's ambassador to the US has said Beijing will not accept a nuclear armed North Korea amid the crisis over Pyongyang's rapidly escalating weapons programme.

Cui Tiankai's comments on Friday came after some experts and observers have said global powers should accept that Pyongyang has nuclear weapons and policy should now be directed at ensuring they do not use them.

Here are three reasons why China is so opposed to Kim Jong-un's regime having nuclear arms:

1. Fears of a regional arms race

Observers say China is extremely wary of its neighbours obtaining a credible nuclear arsenal as it poses an obvious risk to its own security. It has also prompted concerns in Beijing that a regional arms race would develop, with South Korea and Japan feeling the need to obtain their own nuclear weapons.

South Korea's official policy is to pursue a nuclear-free Korean peninsula after giving up its own nuclear weapons programme in the 1970s, although some experts believe it still has the technical capacity and equipment to produce them.

South Korea says its policy remains unchanged, but Deng Yuwen, a senior researcher at the Charhar Institute think tank, wrote in a commentary that Seoul and the US were discussing reintroducing American weaponry with nuclear warheads.

"China will have no choice, but to accept South Korea developing nuclear weapons," Deng wrote.

2. Undermining non-proliferation regime

China is a signatory of the international Non-Proliferation Treaty aimed at limiting the spread of nuclear weapons and championing nuclear disarmament. Japan, the United States and 185 other UN member countries have also signed.

China accepting North Korea as a nuclear state would be a surprise as other emerging nuclear powers such as India and Pakistan have not been accepted under the non-proliferation regime.

"If other emerging nuclear powers such as India, Pakistan and Israel have yet to be accepted as nuclear weapon states under the NPT regime, why should North Korea be an exceptional case?" said Yue Gang, a retired Chinese colonel and military expert.

3. Safety fears

The North Korean regime is bellicose and unpredictable and Deng said Beijing fears its nuclear weapons programme could lead to radiation leaks into its territory.

In a worst-case scenario, the weapons could be turned against China itself, said Deng. "If relations between China and North Korea deteriorate further, no one can guarantee that Kim will not use nuclear weapons against China."

Robert Manning, an international security expert at the US think tank the Atlantic Council, told the South China Morning Post: "I think it's useful for the US to remind China that North Korean missiles go in all directions."